Pityriasis Rubra Pilaris at a Glance
- A papulosquamous disorder of unknown etiology that often progresses to erythroderma and causes a disabling keratoderma of the palms and soles.
- The disease is subclassified into six types including both hereditary and acquired forms.
- The typical features of pityriasis rubra pilaris include follicular hyperkeratosis and a reddish orange, scaling dermatitis with islands of normal skin.
- Confusion with psoriasis presents the major problem in diagnosis, particularly in early phases of the disease.
- Histopathological examination reveals hyperkeratosis, alternating vertical and horizontal parakeratosis, and a mild superficial perivascular lymphocytic infiltrate.
- No single therapy is universally effective, and some cases do not respond to multiple therapies. The most successful treatment options are retinoids, photochemotherapy (PUVA), and antimetabolites (methotrexate).
Pityriasis rubra pilaris is a rare, chronic disorder with an estimated incidence ranging from 1 in 5,000 to 1 in 50,000 dermatology patients. The age distribution is bimodal with peak incidences in the first and fifth decades of life. The disease occurs in all races and affects the sexes equally.1
Although an underlying dysfunction in vitamin A metabolism has been suggested, the etiology and pathogenesis of pityriasis rubra pilaris are still poorly understood. Thus, the role of vitamin A deficiency remains uncertain as attempts to produce keratotic lesions by vitamin A deprivation have been unsuccessful. Moreover, the deficiency of retinol-binding protein as an underlying pathogenic mechanism resulting in inadequate transport of vitamin A to the skin has yet to be ascertained. There are some cases in which pityriasis rubra pilaris may result from immune system dysregulation and abnormal response to various antigenic triggers.2 A report of an exanthematous form of juvenile pityriasis rubra pilaris that followed an upper respiratory infection and initially resembled Kawasaki disease supports the hypothesis of a superantigen-mediated process. Finally, genetic factors with an autosomal dominant pattern of inheritance have been supposed to play a critical role for the induction of pityriasis rubra pilaris. Nevertheless, affected relatives are not observed in the classical acute-onset disease and are infrequent in other variants.
Pityriasis rubra pilaris is generally believed to comprise more than a single entity and a classification scheme based on clinical characteristics and course has been proposed by Griffiths1 (Table 24-1).
Table 24-1 Classification Scheme of Pityriasis Rubra Pilaris (Types I–V According to Griffiths) |Favorite Table|Download (.pdf)
Table 24-1 Classification Scheme of Pityriasis Rubra Pilaris (Types I–V According to Griffiths)
Erythroderma with islands of normal skin (“nappes claires”), follicular hyperkeratosis, waxy diffuse palmoplantar keratoderma
Generalized, beginning on the head and neck, then spreading caudally
Often resolves within an average period of 3 years
Combination of follicular hyperkeratosis and ichthyosiform lesions on the legs, sparse scalp hair
Long duration (>20 years)...